Cobalt-stabilized lithium metal oxide electrodes for lithium batteries

ABSTRACT

An electrode material comprising a composite lithium metal oxide, which in an initial state has the formula: y[xLi 2 MO 3 .(1−x)LiM′O 2 ].(1−y)Li 1+d Mn 2-z-d M″ z O 4 ; wherein 0≤x≤1; 0.75≤y&lt;1; 0&lt;z≤2; 0≤d≤0.2; and z−d≤2. M comprises one or more metal ions that together have an average oxidation state of +4; M′ comprises one or more metal ions that together have an average oxidation state of +3; and M″ comprises one or more metal ions that together with the Mn and any excess proportion of lithium, “d”, have a combined average oxidation state between +3.5 and +4. The Li 1+d Mn 2-z-d  M″ z O 4  component comprises a spinel structure, each of the Li 2 MO 3  and the LiM′O 2  components comprise layered structures, and at least one of M, M′, and M″ comprises Co. Cells and batteries comprising the electrode material also are described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.14/554,762 filed on Nov. 26, 2014, which claims the benefit of U.S.Provisional Application Ser. No. 61/920,283, filed on Dec. 23, 2013,each of which is incorporated by reference in its entirety.

CONTRACTUAL ORIGIN OF THE INVENTION

The United States Government has rights in this invention pursuant toContract No. DE-AC02-06CH11357 between the United States Government andUChicago Argonne, LLC representing Argonne National Laboratory.

FIELD OF THE INVENTION

This invention relates to electrode materials for electrochemical cellsand batteries. Such cells and batteries are used widely to powernumerous devices, for example, portable electronic appliances andmedical, transportation, aerospace, and defense systems.

BACKGROUND

State-of-the-art lithium batteries do not provide sufficient energy topower electric vehicles for an acceptable driving range. This limitationarises because the electrodes, both the anode, typically graphite, andthe cathode, typically, layered LiMO₂ (M=Mn, Co, Ni), spinel LiMn₂O₄ andolivine LiFePO₄, do not offer sufficient capacity or a high enoughelectrochemical potential to meet the energy demands. Approaches thatare currently being adopted to enhance the energy of lithium-ionbatteries include the exploitation of composite cathode structures thatoffer a significantly higher capacity compared to conventional cathodematerials. In particular, lithium-rich and manganese-rich high capacitycathodes, such as xLi₂MnO₃.(1−x)LiMO₂ (M=Mn, Ni, Co) materials (oftenreferred to as ‘layered-layered’ materials, because both the Li₂MnO₃ andLiMO₂ components have layered-type structures) suffer from ‘voltagefade’ on repeated cycling, which reduces the energy output andefficiency of the cell, thereby compromising the management ofcell/battery operation.

There is an ongoing need for new electrode materials to ameliorate theproblems associated with the voltage fade of ‘layered-layered’ electrodematerials. The electrodes, electrochemical cells, and batteries of thisinvention address this need.

SUMMARY OF THE INVENTION

The present invention provides a composite lithium metal oxide electrodematerial comprising a three-component, ‘layered-layered-spinel’composite, which in an initial state (i.e., as prepared) has theformula: y[xLi₂MO₃.(1−x)LiM′O₂].(1−y)Li_(1+d)Mn_(2-z-d) M″_(z)O₄;wherein 0≤x≤1; 0.75≤y<1; 0<z≤2; 0≤d≤0.2; and z−d≤2. M comprises one ormore metal ions that together have a combined average oxidation state of+4 (e.g., Mn, Ti and Zr); M′ comprises one or more metal ions thattogether have a combined average oxidation state of +3 (e.g., Mn and Ni,or Mn, Ni and Co); and M″ comprises one or more metal ions (e.g., Ni,Co, or Ni and Co) that together with the Mn and any excess proportion oflithium, “d”, in the spinel formula above have a combined averageoxidation state between +3.5 and +4; preferably, M″ includes at leastsome Co. The Li_(1+d)Mn_(2-z-d) M″_(z)O₄ component comprises a spinelcrystal structure, each of the Li₂MO₃ and the LiM′O₂ components compriselayered crystal structures, and at least one of M, M′, and M″ comprisesCo. In some embodiments, 0.85≤y<1 or 0.9≤y<1, or 0.85≤y≤0.9. Preferably,0≤x≤0.5. The ‘layered-layered-spinel’ materials of the inventionsurprisingly ameliorate the voltage fade problem associated conventional‘layered-layered’ and ‘layered-spinel’ positive electrode materials inlithium battery applications.

Preferably, M comprises at least one metal selected from the groupconsisting of Mn, Ti and Zr; M′ comprises at least one metal selectedfrom the group consisting of Mn, Ni, and Co, and M″ comprises at leastone metal selected from the group consisting of Ni, and Co. Optionally,each of M and M′ can independently further comprise at least one metalselected from the group consisting of Al, Mg, and Li; M can furthercomprise at least one metal selected from the group consisting of afirst or second row transition metal other than Mn, Ti, and Zr; M′ canfurther comprise at least one metal selected from the group consistingof a first or second row transition metal other than Mn, Ni and Co,provided that the average oxidation state of the combined M ions is +4,and the average oxidation state of the combined M′ ions is +3; and M″can further comprise at least one metal selected from the groupconsisting of Al, Mg, and a first or second row transition metal otherthan Ni and Co (e.g., Ti, Fe, Zr) such that the M″ ions in the spinelformula Li_(1-d)M_(2-z-d) M″_(z)O₄ have a combined average oxidationstate between +3.5 and +4.

In some embodiments, the spinel component, Li_(1+d)Mn_(2-z-d) M″_(z)O₄,is a lithium-rich spinel (i.e., including an excess proportion of Li,represented by “d”, where 0<d≤0.2). Preferably, the proportion, z, of M″is in the range of 0.2<z≤0.6; and M″ comprises Ni, Co, or a combinationthereof. For example, M″ can comprise at least one metal selected fromthe group consisting of Ni and Co; d>0; and 2−d−z>0. In some otherpreferred embodiments, M is Mn; M′ comprises Mn and Ni; and the spinelcomponent, Li_(1+d)Mn_(2-z-d)M″_(z)O₄, comprises Mn, Ni, and Co. Forexample, M″ can comprise at least one metal selected from the groupconsisting of Ni and Co; d>0; and 2−d−z>0.

The present invention also provides a layered-layered-spinel electrodematerial in which M″ comprises Ni and Co; Co constitutes about 1 atompercent to about 30 atom percent of transition metals in the spinelcomponent, Li_(1+d)Mn_(2-z-d)M″_(z)O₄; and the combination of Mn and Niconstitutes about 70 atom percent to about 99 atom percent of thetransition metals in the spinel component. Preferably, the combinationof Mn and Ni constitutes about 80 atom percent of the transition metalsin the spinel component and Co constitutes about 20 atom percent of thetransition metals in the spinel component. In a preferred embodiment,the spinel component constitutes about 50 atom percent Mn, about 30 atompercent Ni, and about 20 atom percent Co, based on the total transitionmetals in the spinel component.

The composition of the layered-layered-spinel electrodes of thisinvention can therefore be tailored for optimum electrochemicalperformance. In particular, it has been discovered that the cobaltcontent plays a significant role in determining the performance of thesematerials.

In a particular embodiment of the invention, the Co content in they[xLi₂MO₃.(1−x)LiM′O₂].(1−y)Li_(1+d)Mn_(2-z-d) M″_(z)O₄ electrodecomprises more than 50% of the combined M, M′, and M″ content.Alternatively, the Co content can comprise less than 50% of the combinedM, M′, and M″ content. In yet another embodiment, the Ni content in they[xLi₂MO₃.(1−x)LiM′O₂].(1−y)Li_(1+d)Mn_(2-z-d) M″_(z)O₄ electrode cancomprise more than 50% of the combined M, M′, and M″ content, forexample, 60%, 70%, 80% or 90%.

In some embodiments, x=0, and the electrode material comprises atwo-component layered-spinel composite compound, which in an initialstate has the formula: yLiM′O₂.(1−y)Li_(1+d)Mn_(2-z-d)M″_(z)O₄; wherein0.75≤y<1; 0<z≤2; 0≤d≤0.2; z−d≤2; M′ comprises one or more metal ionsthat together have a combined average oxidation state of +3; and M″comprises one or more metal ions that together with the Mn and excessproportion, d, of lithium, have a combined average oxidation state of+3.5; wherein the LiM″O₄ component comprises a spinel crystal latticestructure; the LiM′O₂ component thereof comprises a layered crystallattice structures; and at least one of M′ and M″ comprises Co. In someembodiments of the layered-spinel composite, 0.85≤y<1; wherein 0.9≤y<1,or 0.85<y≤0.9.

In some embodiments of the layered-spinel material, each of M′ comprisesat least one metal selected from the group consisting of Mn, Ni, and Co;and M″ comprises at least one metal selected from the group consistingof Ni and Co. Optionally, M′ further comprises at least one metalselected from the group consisting of Al, Mg, Li, and a first or secondrow transition metal other than Mn, Ni and Co; and M″ further comprisesat least one metal selected from the group consisting of Al, Mg, and afirst or second row transition metal other than Mn, Ni and Co.

In some embodiments of the layered-spinel material, 0<d≤0.2; 0.2<z≤0.6;and M″ comprises Ni, Co, or a combination thereof.

In some other embodiments of the layered-spinel material, M″ comprisesat least one metal selected from Ni and Co.

In some other embodiments of the layered-spinel material, M′ comprisesMn and Ni, or Mn, Ni and Co.

In some embodiments of the layered-spinel material, the spinelcomponent, Li_(1+d)Mn_(2-z-d)M″_(z)O₄, comprises Mn, Ni, and Co. Forexample, M′ comprises Mn and Ni; and the spinel component,Li_(1+d)Mn_(2-z-d)M″_(z)O₄, comprises Mn, Ni, and Co.

In some other embodiments of the layered-spinel material, M″ comprisesat least one metal selected from the group consisting of Ni and Co; d>0;and 2−d−z>0.

In one preferred embodiment of the layered-spinel material, M″ comprisesNi and Co; Co constitutes about 1 atom percent to about 30 atom percentof transition metals in spinel component, Li_(1+d)Mn_(2-z-d)M″_(z)O₄;and the combination of Mn and Ni constitutes about 70 atom percent toabout 99 atom percent of the transition metals in the spinel component.For example, the combination of Mn and Ni can constitute about 80 atompercent of the transition metals in the spinel component, and Co canconstitute about 20 atom percent of the transition metals in the spinelcomponent. Alternatively, the spinel component can constitute about 50atom percent Mn, about 30 atom percent Ni, and about 20 atom percent Coof the transition metals in the spinel component.

The Li, Mn, M′ and M″ cations of the layered-spinel material can bepartially disordered over the octahedral and tetrahedral sites of thelayered and spinel components of the composite lithium metal oxidestructure.

In another aspect, the present invention provides a positive electrodefor a lithium electrochemical cell comprising layered-layered-spineland/or layered-spinel electrode material, preferably in contact with ametal current collector. If, desired, the layered-layered-spinel and/orlayered-spinel materials can be formulated with another active electrodematerial, such as carbon. The electrode is useful as a positiveelectrode in lithium electrochemical cells and batteries.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention consists of certain novel features and a combination ofparts hereinafter fully described, illustrated in the accompanyingdrawings, it being understood that various changes in the details may bemade without departing from the spirit, or sacrificing any of theadvantages of the present invention.

FIG. 1 depicts a Li₂MO₃-LiM′O₂—LiM″₂O₄ phase diagram, in which Li₂MO₃,LiM′O₂, and Li_(1+d)Mn_(2-z-d) M″_(z)O₄ (represented for simplicity asLiM″₂O₄, i.e., where d is 0 and M″ includes the Mn portion of thespinel) are the layered, layered, and spinel components of alayered-layered-spinel electrode material.

FIG. 2 depicts (a) the electrochemical cycling behavior and voltage fadeand (b) corresponding dQ/dV plots of a ‘layered-layered’0.5Li₂MnO₃.0.5LiMn_(0.5)Ni_(0.5)O₂ electrode in a lithium half-cell,charged and discharged between 4.6 and 2.0 V.

FIG. 3 depicts (a) the electrochemical cycling behavior and (b)corresponding dQ/dV plots of a ‘layered-layered-spinel’ electrode ofthis invention derived from a lithium-deficient0.25Li₂MnO₃.0.75LiMn_(0.375)Ni_(0.375) Co_(0.25)O₂ composition togenerate 15% spinel in the composite structure.

FIG. 4 depicts the X-ray diffraction patterns of (left)‘layered-layered’ 0.25Li₂MnO₃.0.75 LiMn_(0.375)Ni_(0.375) Co_(0.25)O₂products when synthesized from a metal oxalate and Li₂MnO₃ precursors,and (right) layered-layered spinel products synthesized fromlithium-deficient compositions of 0.25Li₂MnO₃.0.75LiMn_(0.375)Ni_(0.375)Co_(0.25)O₂.

FIG. 5 depicts (top) the electrochemical profiles of lithium half cellsin which the 0.25Li₂MnO₃.0.75 LiMn_(0.375)Ni_(0.375) Co_(0.25)O₂ cathodewas prepared from (left) oxalate and (right) Li₂MnO₃ precursors, thecells being charged and discharged between 4.45 and 2.0 V, after aninitial activation charge to 4.6 V, at 15 mA/g.

FIG. 6 depicts (top) the electrochemical profiles of lithium half cellsin which the ‘layered-layered-spinel’ cathode with 15% spinel wasderived from a 0.25Li₂MnO₃.0.75LiMn_(0.375)Ni_(0.375) Co_(0.25)O₂composition prepared from (left) oxalate and (right) Li₂MnO₃ precursors,the cells being charged and discharged between 4.45 and 2.0 V, after aninitial activation charge to 4.6 V, at 15 mA/g.

FIG. 7 depicts the first-cycle discharge capacity (▪) and first-cycleefficiency (□) as a function of cathode composition, x, inLi_(x)Mn_(0.53125)Ni_(0.28125)Co_(0.18750)O₆ and the correspondingtarget spinel content as a percentage in the ‘layered-layered-spinel’cathode.

FIG. 8 provides plots of voltage versus capacity (Panel A) andnormalized capacity (Panel B) for samples of 0.5Li₂MnO₃.0.5LiCoO₂prepared at temperatures ranging from 400 to 900° C.

FIG. 9 provides plots of first cycle charge capacity, dischargecapacity, and efficiency for samples using a layered-layered template,i.e., a pristine layered-layered0.1Li₂MnO₃.0.9LiMn_(0.4)Ni_(0.55)Co_(0.05)O₂ composition, anacid-treated pristine sample with additional Co annealed at 450° C. forthree hours, and an acid-treated pristine sample with additional Coannealed at 750° C. for six hours.

FIG. 10 provides plots of voltage versus capacity for selectedacid-treated 0.1Li₂MnO₃.0.9LiMn_(0.4)Ni_(0.55)Co_(0.05)O₂ materials.

FIG. 11 shows the electrochemical charge/discharge profiles for the1^(st), 2^(nd), 5^(th), and 10^(th) cycles of aLi/0.25Li₂MnO₃.0.75LiMn_(0.125) Co_(0.125)Ni_(0.75)O₂(‘layered-layered’) half-cell.

FIG. 12 shows the corresponding dQ/dV plots for the 2^(nd), 5^(th) and10^(th) cycles for the cell of FIG. 11.

FIG. 13 shows the capacity vs. cycle number plots for the first 20charge/discharge cycles of the cell of FIG. 11.

FIG. 14 depicts the electrochemical charge/discharge profiles for the1^(st), 2^(nd), 5^(th), and 10^(th) cycles of aLi/0.85[0.25Li₂MnO₃.0.75LiMn_(0.125)Co_(0.125)Ni_(0.75)O₂].0.15LiM″₂O₄(‘layered-layered-spinel’) half-cell.

FIG. 15 shows the corresponding dQ/dV plots for the 2^(nd), 5^(th) and10^(th) cycles of the cell of FIG. 14.

FIG. 16 depicts the capacity vs. cycle number plots for the first 10charge/discharge cycles of the cell of FIG. 14.

FIG. 17 depicts a schematic representation of an electrochemical cell.

FIG. 18 depicts a schematic representation of a battery consisting of aplurality of cells connected electrically in series and in parallel.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

This invention relates to cobalt-stabilized lithium-metal oxideelectrodes that fall within the scope of structurally compatible,composite ‘layered-layered’ and ‘layered-spinel’ materials that containa layered Li₂MnO₃ component. Selected compositions of these materialshave been discovered that appear to arrest a voltage fade phenomenonwhich occurs when state-of-the-art ‘layered-layered’ and‘layered-spinel’ electrode materials are repeatedly cycled in lithiumcells. The preferred precursor compound for synthesizing the improvedcompounds and compositions of the invention comprises Li₂MnO₃ (or inconventional layered notation Li[Li_(1/3)Mn_(2/3)]O₂).

Broadly speaking, it has been discovered that the voltage fade ofhigh-capacity ‘layered-layered’ xLi₂MnO₃.(1−x)LiMO₂ electrodes, in whichM is a metal cation is comprised, typically of Mn, Ni and Co, can besuppressed by introducing a spinel component into the ‘layered-layered’structure by careful selection and control of the Li₂MnO₃ and Co contentand overall composition of the resulting ‘layered-layered-spinel’products. In a general embodiment, the materials of the invention can bedefined on a ‘layered-layered-spinel’ Li₂MO₃—LiM′O₂—LiM″₂O₄ phasediagram, shown schematically in FIG. 1, in which Li₂MO₃, LiM′O₂, andLi_(1+d)Mn_(2-z-d) M″_(z)O₄ (represented in the diagram as LiM″₂O₄, forsimplicity, i.e., where d is 0 and M″ includes the Mn portion of thespinel) are the layered, layered, and spinel components, respectively,that described the overall composition of the electrode within theLi₂MO₃-LiM′O₂—LiM″₂O₄ phase diagram; and where M is one or more metalcations with a combined average tetravalent oxidation state, preferablyMn⁴⁺; M′ is one or more metal cations with a combined average trivalentoxidation state, preferably comprising manganese, nickel and cobaltions, and M″ comprises one or more metal cations with a combined averageoxidation state of between +3.5 and +4.0, preferably comprisingmanganese, nickel and cobalt ions, optionally with lithium ions. Forexample, the average oxidation state of a Li_(1+d)Mn_(2-z-d)M″_(z)O₄component in which d=0 and z=0 would be +3.5, whereas for d=0.333 andz=0 (i.e., Li_(1.333)Mn_(1.667)O₄), it would be +4.0.

The composite ‘layered-layered-spinel’ electrode structures andmaterials of this invention (which can, in general, be regarded overallas a composite structure with both layered and spinel character), havethe advantage of providing a voltage profile with both the slopingcharacter of the layered components and the voltage plateaus of thespinel components, thus smoothing the overall voltage profile of highcapacity, structurally-integrated, ‘composite’ layered-spinel electrodesof this invention. The spinel electrode materials of this invention arebroad in compositional scope and structure. In an ideal LiM″₂O₄ spinelstructure, the metal cations are distributed in octahedral sites inalternating close-packed oxygen layers in a 3:1 ratio of transitionmetals to Li, whereas, in an ideal LiM′O₂ layered structure, the M′transition metal cations occupy all the octahedral sites in alternatinglayers, without any Li being present in those layers. Therefore, in thecomposite layered-spinel structures of this invention, the ratio ofmetal cations in alternating layers of the close-packed oxygen array canvary within the structure from the 3:1 transition metal to Li ratio ofan ideal spinel configuration to the corresponding ideal layeredconfiguration with no lithium in the transition metal layers.Furthermore, the Li, Mn, M, M′ and M″ cations of the spinel and layeredelectrode materials of this invention can be partially disordered overthe octahedral and tetrahedral sites of the layered and spinelcomponents of the compositey[xLi₂MO₃.(1−x)LiM′O₂].(1−y)Li_(1+d)Mn_(2-z-d) M″_(z)O₄ lithium metaloxide structure, yielding complex cation arrangements in the spinel andlayered components and in the overall and highly complex‘layered-layered-spinel’ composite structures. In some instances, thestructural complexity of the electrodes of the invention makes itdifficult to distinguish the individual components from one another,particularly when the intergrown layered Li₂MO₃ and LiM′O₂ componentsare disordered within a single, structurally-compatible close-packedoxide array, in which case the electrode composition can be simplyregarded as, and represented, by a ‘layered-spinel’ structure.

The principles of the invention are embodied in FIG. 2 and FIG. 3. FIG.2, panel (a), shows the electrochemical cycling behavior and voltagefade of a typical ‘layered-layered’ 0.5Li₂MnO₃.0.5LiMn_(0.5)Ni_(0.5)O₂electrode in a lithium half-cell, when the cells are charged anddischarged continuously between 4.6 and 2.0 V. FIG. 2, panel (b), showsthe corresponding dQ/dV plots of the data in panel (a). These dataclearly highlight the electrochemical and concomitant structural decayof the xLi₂MnO₃.(1−x)LiMO₂ electrode that leads to energy loss andinefficiency of the lithium cell on repeated cycling.

The electrochemical and corresponding dQ/dV plots of an advanced‘layered-layered-spinel’ electrode of this invention derived from alithium-deficient 0.25Li₂MnO₃.0.75 LiMn_(0.375)Ni_(0.375)Co_(0.25)O₂precursor to generate 15% spinel in the composite structure are shown inFIG. 3, panels (a) and (b), respectively. This electrode was activatedby an initial charge/discharge cycle between 4.6 and 2.0 V and thensubsequently charged and discharged between 4.45 and 2.0 V. The voltageprofiles (FIG. 3, panel (a)) and corresponding dQ/dV plots (FIG. 3,panel (b)) indicate remarkable cycling stability relative to those inFIG. 2 without any significant redox process occurring below 3.5 V,while still generating between 180 and 200 mAh/g for twenty cycles. Thissurprisingly improved performance is attributed to the spinel componentwithin the composite structure, notably cobalt-rich spinel components,LiM₂O₄, in which M is predominantly Co and Ni relative to Mn and Li. Inthis respect, it is to be noted that a Li[Co₂]O₄ spinel is known toaccommodate lithium at approximately 3.4 V, which emphasizes theadvantage of using a cobalt or cobalt-substituted Li[Co_(2-x)M_(x)]O₄spinel to stabilize the cycling performance of ‘layered-layered’electrodes.

Similarly, in a preferred embodiment of the invention, when x=0, the‘layered-spinel’ yLiM′O₂.(1−y)Li_(1+d)Mn_(2-z-d) M″_(z)O₄ electrodestructure has a composition in which M″ comprises at least one metalselected from the group consisting of Ni, and Co.

The electrode compositions and structures of this invention can besynthesized by using Li₂MnO₃ as a precursor and reacting it with therequired amount of Ni and Co in solution followed by a heat-treatmentstep, as described by Croy et al., in Electrochemistry Communications,Volume 13, pages 1063-1066 (2011). For example, a ‘layered-layered’product with a targeted composition0.25Li₂MnO₃.0.75LiMn_(0.375)Ni_(0.375)Co_(0.25)O₂ can be prepared byreacting a Li₂MnO₃ precursor with the stoichiometrically-requiredamounts of nickel and cobalt nitrates in a 0.1 M solution of HNO₃, andthen stirring the mixture overnight at room temperature. Thereafter, theliquid from the solution is evaporated at approximately 70° C., and theresulting solid product collected and ground to a powder. The powder isthen annealed at about 850° C. for about 24 hours in air. Variations insynthesis parameters, e.g., temperature, dwell times, rates of cooling,etc., can be used to optimize the structures and electrochemicalproperties of the materials of this invention for a given application oruse. In order to synthesize ‘layered-layered-spinel’ products of thisinvention, the same procedure is followed, as described above, but usinga smaller amount of lithium than is required for the ‘layered-layered’composition, which drives the composition of the final product towardthe LiM″₂O₄ spinel apex of the phase diagram in FIG. 1, therebyresulting in the ‘layered-layered-spinel’ products. Alternatively, thecompositions of the advanced materials of this invention can besynthesized by other processing methods that are known in the art, forexample, by sol-gel and precipitation processing techniques usingprecursors that decompose during synthesis, such as metal hydroxides,carbonates and oxalates, or by solid state reactions, thereby broadeningthe scope of this invention.

In a particular embodiment of the invention, the Co content in they[xLi₂MO₃.(1−x)LiM′O₂].(1−y)Li_(1+d)Mn_(2-z-d) M″_(z)O₄ electrodecomprises more than 50% of the combined M, M′, and M″ content.Alternatively, the Co content can comprise less than 50% of the combinedM, M′, and M″ content. In yet another embodiment, the Ni content in they[xLi₂MO₃.(1−x)LiM′O₂].(1−y)Li_(1+d)Mn_(2-z-d) M″_(z)O₄ electrode cancomprise more than 50% of the combined M, M′, and M″ content, forexample, 60%, 70%, 80% or 90%.

Specific examples of the processing methods that were employed tosynthesize the electrodes of this invention are:

-   -   1. (NiMnCo)C₂O₄ (i.e., metal oxalate) precursors were prepared        from NiSO₄.6H₂O, MnSO₄.H₂O, CoSO₄.7H₂O, and Na₂C₂O₄ using the        required ratios of Ni, Mn and Co for a targeted stoichiometry in        the final product (the ‘oxalate method’). An aqueous solution        containing the required stoichiometric amounts of metal sulfates        was added under stirring into a solution of sodium oxalate. The        solution was then stirred for about 3 hours at about 70° C. The        co-precipitated powder was filtered, washed, and dried in air at        about 105° C. The dried powders were thoroughly mixed with        stoichiometric amounts of lithium carbonate and annealed at        about 450° C. for about 12 hours in air, followed by grinding        and an annealing step at about 750° C. for about 12 hours (also        in air) to prepare materials with a desired composition. Other        annealing conditions included no intermediate firing step,        different annealing times and different temperatures.    -   2. Materials from Li₂MnO₃ precursors were prepared by the        following procedure: Li₂MnO₃ was added under stirring into a 0.1        M HNO₃ solution at room temperature (the ‘Li₂MnO₃ method’). The        required amounts of Ni(NO₃)₂.6H₂O, Co(NO₃)₂.6H₂O, and LiNO₃ for        a desired stoichiometry in the final product were added to the        solution and subsequently stirred overnight. The solution was        then heated to dryness at approximately 80° C., then the solid        product was ground and annealed in air at about 850° C. for        about 24 hours.

The versatility in synthesizing the ‘layered-layered-spinel’ electrodematerials of this invention are demonstrated in FIGS. 4 to 6 by methodsusing (1) metal oxide precursors and (2) a Li₂MnO₃ template into whichthe required metal cations and oxygen are introduced to create thecomposite structures as described by Croy et al., in ElectrochemistryCommunications, Volume 13, pages 1063-1066 (2011).

For example, FIG. 4 (left) shows the powder X-ray diffraction patterns(CuKα radiation) of a ‘layered-layered’0.25Li₂MnO₃.0.75LiMn_(0.375)Ni_(0.375)Co_(0.25)O₂ composition (i.e.,targeting 0% spinel in the structure) using manganese, nickel and cobaltoxalate precursors and the same composition using a Li₂MnO₃ template forcomparison; FIG. 4 (right) shows the powder X-ray diffraction patternsof a ‘layered-layered-spinel product with 15% spinel derived from0.25Li₂MnO₃.0.75LiMn_(0.375)Ni_(0.375)Co_(0.25)O₂ by reducing thelithium content in the starting precursors by 9%. These X-raydiffraction patterns are similar, highlighting the difficulty indifferentiating the ‘layered-layered’ structures from‘layered-layered-spinel’ derivatives by routine X-ray diffractionmethods.

Cathodes for the electrochemical tests were prepared by coating Al foilwith a slurry containing 82 percent by weight (wt %) of the oxidepowder, 8 wt % SUPER P carbon (TIMCAL Ltd.), and 10 wt % polyvinylidenedifluoride (PVDF) binder in NMP and assembled in coin cells (size 2032).The cells contained a metallic lithium anode. The electrolyte was a 1.2M solution of LiPF₆ in a 3:7 mixture of ethylene carbonate (EC) andethyl methyl carbonate (EMC). Coin cells were assembled in a gloveboxunder an inert argon atmosphere.

FIG. 5 shows (top, left and right) the electrochemical cycling profilesand (bottom) the corresponding dQ/dV plots ofLi/0.25Li₂MnO₃.0.75LiMn_(0.375)Ni_(0.375)Co_(0.25)O₂ cells, in which thecathode was synthesized by the oxalate and Li₂MnO₃ methods,respectively, when cycled between 4.45 and 2.0 V after an initialactivation charge to 4.6 V. Both cells show exceptional stability overthis voltage range with insignificant voltage fade relative to the dataof the ‘layered-layered’ 0.5Li₂MnO₃.0.5LiMn_(0.5)Ni_(0.5)O₂ electrodeshown in FIG. 2.

FIG. 6 shows (top, left and right) the electrochemical cycling profilesand (bottom) the corresponding dQ/dV plots of lithium cells in which the‘layered-layered-spinel’ cathode, when synthesized by the oxalate andLi₂MnO₃ methods, respectively, was derived from a0.25Li₂MnO₃.0.75LiMn_(0.375)Ni_(0.375)Co_(0.25)O₂ composition byreducing the lithium in the composition by 9%, when cycled between 4.45and 2.0 V after an initial activation charge to 4.6 V. Both cells cycledwith exceptional stability over this voltage range, delivering a steadycapacity between 180 and 190 mAh/g at an average voltage ofapproximately 3.54 V with insignificant voltage fade relative to thedata of the ‘layered-layered’ 0.5Li₂MnO₃.0.5LiMn_(0.5)Ni_(0.5)O₂electrode shown in FIG. 2.

A series of ‘layered-layered-spinel’ electrode compositions with varyingspinel content, synthesized by the ‘oxalate method’, was investigatedelectrochemically. For one experiment, electrodes were prepared by usingless lithium than would normally be used for synthesizing a‘layered-layered’ electrode of nominal composition 0.25Li₂MnO₃.0.75LiMn_(0.375)Ni_(0.375)Co_(0.250)O₂ in which the Mn:Ni:Co ratio is0.53125:0.28125:0.18750; this ‘layered-layered-spinel’ electrode isnormalized to read ‘Li_(x)Mn_(0.53125)Ni_(0.28125)Co_(0.18750)O_(δ)’ forconvenience and simplicity, with the value of x=1.25 and δ=2.25representing the parent ‘layered-layered’ composition0.25Li₂MnO₃.0.75LiMn_(0.375)Ni_(0.375)Co_(0.250)O₂. A plot offirst-cycle capacity and first-cycle efficiency vs. lithium (spinel)content of a lithium cell containing the‘Li_(x)Mn_(0.53125)Ni_(0.28125)Co_(0.18750)O_(δ)’ electrode is shown inFIG. 7. The top x-axis shows the increasing target spinel content as afunction of decreasing lithium content. The electrodes were firstcharged to 4.6 V and discharged to 2.0 V in lithium coin cells. The plotof solid squares indicates that the electrode capacity reaches a maximumby lowering the lithium content corresponding to spinel content ofapproximately 6%, after which the electrode capacity decreases, inaccordance with a significant advantage of the layered-layered-spinelelectrodes of this invention over conventional layered-layeredelectrodes. Lowering the lithium content, thereby increasing the spinelcontent, also has the significant advantage of increasing thefirst-cycle efficiency of the cell (open squares).

The invention extends to include lithium metal oxide electrode materials(e.g., lithium-rich spinels, layered oxides, and the like) with surfacemodification, for example, with metal-oxide, metal-fluoride ormetal-phosphate layers or coatings to protect the electrode materialsfrom highly oxidizing potentials in the cells and from other undesirableeffects, such as electrolyte oxidation, oxygen loss, and/or dissolution.Such surface protection enhances the surface stability, rate capabilityand cycling stability of the electrode materials.

In some embodiments, individual particles of a powdered lithium metaloxide composition, a surface of the formed electrode, or both, arecoated or treated, e.g., in situ during synthesis, for example, with ametal oxide, a metal fluoride, a metal polyanionic material, or acombination thereof, e.g., at least one material selected from the groupconsisting of (a) lithium fluoride, (b) aluminum fluoride, (c) alithium-metal-oxide in which the metal is selected preferably, but notexclusively, from the group consisting of Al and Zr, (d) alithium-metal-phosphate in which the metal is selected from the groupconsisting preferably, but not exclusively, of Fe, Mn, Co, and Ni, and(e) a lithium-metal-silicate in which the metal is selected from thegroup consisting preferably, but not exclusively, of Al and Zr. In apreferred embodiment of the invention, the constituents of the treatmentor coating, such as the aluminum and fluoride ions of an AlF₃ coating,the lithium and phosphate ions of a lithium phosphate coating, or thelithium, nickel and phosphate ions of a lithium-nickel-phosphate coatingcan be incorporated in a solution that is contacted with thehydrogen-lithium-manganese-oxide material or the lithium-manganese-oxideprecursor when forming the electrodes of this invention. Alternatively,the surface may be treated with fluoride ions, for example, using NH₄F,in which case, the fluoride ions may substitute for oxygen at thesurface or at least partially within the bulk of the electrodestructure.

Preferably, a formed positive electrode comprises at least about 50percent by weight (wt %) of a powdered lithium metal oxide compositioncomprising the lithium-rich spinel material, and an electrochemicallyinert polymeric binder (e.g., polyvinylidene difluoride; PVDF).Optionally, the positive electrode can comprise up to about 40 wt %carbon (e.g., carbon back, graphite, carbon nanotubes, carbonmicrospheres, carbon nanospheres, or any other form of particulatecarbon).

In another example, the data in FIG. 8, Panel A, show the first cyclevoltage profiles when cycled between 4.6 and 2 V at 15 mA/g for0.5Li₂MnO₃.0.5LiCoO₂ compositions made at temperatures in the range of400 to 900° C. The incorporation of a “low-temperature” LiCoO₂ lithiatedspinel component (i.e., Li₂[Co₂]O₄) into a layered-layered compositestructure (i.e., control of stabilizing Co in the Li layer) is evidentin the 400° C. and 500° C. samples, which exhibited a 3.4 V plateau.Above these temperatures, it appears that the Co migrates into thetransition metal layer to induce greater layered character to theelectrode. FIG. 8, Panel B, shows the normalized first cycle dischargevoltage profile which clearly illustrates the presence of the 3.4 Vplateau.

In another embodiment, the Co can be introduced into a series of layeredNi/Mn/Co and layered-layered compositions with increasing Li content(i.e., increasing ‘layered-layered’ character). The material prepared atlower synthesis temperature showed an increase in 3.4 V plateau capacityassociated with stabilizing Co in the Li layer in a Ni containing oxide.

The compositions and structures of this invention can be synthesized byvarious processing methods, such as acid treatment of a layered,two-component, layered-layered material, or a three-component,layered-layered-spinel template or precursor as described by Croy et.al., in Electrochemistry Communications, Volume 13, pages 1063-1066(2011). For example, FIG. 9 shows the first cycle charge capacity,discharge capacity, and efficiency for samples using a layered-layeredtemplate: (1) a pristine layered-layered0.1Li₂MnO₃.0.9LiMn_(0.4)Ni_(0.55)Co_(0.05)O₂ composition, (2) an acidtreated pristine sample with additional Co annealed at 450° C. for threehours, and (3) an acid treated pristine sample with additional Coannealed at 750° C. for six hours. All three samples deliverapproximately 200 to 205 mAh/g first cycle discharge capacity whencycled between 4.6 and 2 V at 15 mA/g. The addition of stabilizing Co atlow temperatures improved the first cycle efficiency without sacrificingdischarge capacity.

FIG. 10 shows the first cycle voltage profiles for the samples from FIG.9 plus additional acid treated samples with additional (50%) Co. Theacid treatment process did not remove significant Li content, asevidenced by the similar discharge capacity for all samples. The lowertemperature samples (450° C.) exhibited a 3.4 V plateau attributed tostabilizing Co in the Li layer, whereas the higher temperature sample(750° C.) did not. A significant advantage of having cobalt in thelithium layer is that it can impart the characteristic discharge voltageof a LiCo₂O₄ spinel at 3.4 V, which can be used as an end-of-dischargeindicator for the electrodes of this invention. By analogy, theinvention can be extended to include electrodes that contain, forexample, a LiNi₂O₄ spinel component, stabilized by the layered componentof the composite structure, which is believed would provide an elevateddischarge voltage relative to LiMn₂O₄ (˜2.9 V), similar to a LiCo₂O₄spinel, or a material such as LiCo_(2-x)Ni_(x)O₄, LiCo_(2-x-y)Ni_(x)Mn_(z)O₄, and the like.

In another example, a metal oxalate precursor with the composition(Ni_(0.5625)Mn_(0.34375)Co_(0.09375))C₂O₄ was prepared according toMethod 1, described earlier, from NiSO₄.6H₂O, MnSO₄.H₂O, CoSO₄.7H₂O, andH₂C₂O₄ using the required ratios of Ni, Mn and Co for the targetedstoichiometry in the final product. The dried powders were thoroughlymixed with stoichiometric amounts of lithium carbonate and annealed atabout 850° C. for about 24 hours in air to prepare materials with acomposition corresponding to a ‘layered-layered’ composition,0.25Li₂MnO₃.0.75LiMn_(0.125)Co_(0.125)Ni_(0.75)O₂ and to a‘layered-layered-spinel’ composition targeting 15% spinel, i.e.,0.85[0.25Li₂MnO₃.0.75LiMn_(0.125)Co_(0.125)Ni_(0.75)O₂].0.15LiM″₂O₄. TheNi to (Co+Mn) ratio in this electrode is approximately 56:44, i.e., theNi content comprises more than 50% of the combined M, M′, and M″content, in accordance with one embodiment of the invention. Cathodesfor the electrochemical tests were prepared and evaluated in coin cellsas described earlier; for these experiments, the Al foil currentcollector was coated with a slurry containing 84 percent by weight (wt%) of the oxide powder, 8 wt % SUPER P carbon (TIMCAL Ltd.), and 8 wt %polyvinylidene difluoride (PVDF) binder in NMP.

FIG. 11 shows the electrochemical charge/discharge profiles for the1^(st), 2^(nd), 5^(th), and 10^(th) cycles of aLi/0.25Li₂MnO₃.0.75LiMn_(0.125) Co_(0.125)Ni_(0.75)O₂(‘layered-layered’) half-cell. FIG. 12 shows the corresponding dQ/dVplots for the 2^(nd), 5^(th) and 10^(th) cycles. FIG. 13 shows thecapacity vs. cycle number plots for the first 20 charge/discharge cyclesof the cell.

FIG. 14 depicts the electrochemical charge/discharge profiles for the1^(st), 2^(nd), 5^(th), and 10^(th) cycles of aLi/0.85[0.25Li₂MnO₃.0.75LiMn_(0.125)Co_(0.125)Ni_(0.75)O₂].0.15LiM″₂O₄(‘layered-layered-spinel’) half-cell. FIG. 15 shows the correspondingdQ/dV plots for the 2^(nd), 5^(th) and 10^(th) cycles. FIG. 16 depictsthe capacity vs. cycle number plots for the first 10 charge/dischargecycles of the cell.

Both cells were charged and discharged between 4.45 and 2.5 V, after aninitial activation charge to 4.6 V, at 15 mA/g. These data clearlydemonstrate the significantly superior electrochemical properties of the‘layered-layered-spinel’ electrode, relative to the ‘layered-layered’electrode in accordance with the principles of the invention. Inparticular, the ‘layered-layered-spinel’ electrode (targeting 15%spinel) delivers a capacity of 207 mAh/g after 10 cycles, which is 7.2%greater than the corresponding 193 mAh/g delivered by the‘layered-layered’ (0% spinel) electrode. Moreover, the cycling stabilityof the ‘layered-layered-spinel’ electrode, as reflected by a 5.6%capacity loss over the first ten cycles of the cell, is significantlysuperior to that of the ‘layered-layered’ electrode (6.5% capacity loss)as shown in Table 1.

TABLE 1 0% spinel 15% spinel 1^(st) cycle discharge (mAh/g) 205.84219.94 5^(th) cycle discharge (mAh/g) 194.25 208.47 10^(th) cycledischarge (mAh/g) 192.71 207.58 20^(th) cycle discharge (mAh/g) 190.35N/AExemplary Electrochemical Cell and Battery.

A detailed schematic illustration of a lithium electrochemical cell 10of the invention is shown in FIG. 17. Cell 10 comprises negativeelectrode 12 separated from positive electrode 16 by a separator 14saturated with the electrolyte, all contained in insulating housing 18with suitable terminals (not shown) being provided in electronic contactwith negative electrode 12 and positive electrode 16 of the invention.Positive electrode 16 comprises metallic collector plate 15 and activelayer 17 comprising the cobalt-stabilized lithium metal oxide materialdescribed herein. FIG. 18 provides a schematic illustration of oneexample of a battery in which two strings of electrochemical cells 10,described above, are arranged in parallel, each string comprising threecells 10 arranged in series.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. The terms “consisting of” and“consists of” are to be construed as closed terms, which limit anycompositions or methods to the specified components or steps,respectively, that are listed in a given claim or portion of thespecification. In addition, and because of its open nature, the term“comprising” broadly encompasses compositions and methods that “consistessentially of” or “consist of” specified components or steps, inaddition to compositions and methods that include other components orsteps beyond those listed in the given claim or portion of thespecification. Recitation of ranges of values herein are merely intendedto serve as a shorthand method of referring individually to eachseparate value falling within the range, unless otherwise indicatedherein, and each separate value is incorporated into the specificationas if it were individually recited herein. All numerical values obtainedby measurement (e.g., weight, concentration, physical dimensions,removal rates, flow rates, and the like) are not to be construed asabsolutely precise numbers, and should be considered to encompass valueswithin the known limits of the measurement techniques commonly used inthe art, regardless of whether or not the term “about” is explicitlystated. All methods described herein can be performed in any suitableorder unless otherwise indicated herein or otherwise clearlycontradicted by context. The use of any and all examples, or exemplarylanguage (e.g., “such as”) provided herein, is intended merely to betterilluminate certain aspects of the invention and does not pose alimitation on the scope of the invention unless otherwise claimed. Nolanguage in the specification should be construed as indicating anynon-claimed element as essential to the practice of the invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. An electrode materialcomprising a two-component, structurally integrated layered-spinelcomposite lithium metal oxide, which in an initial state has theformula:yLiM′O₂.(1−y)Li_(1+d)Mn_(2-z-d)M″_(z)O₄; wherein: 0.75≤y<1; 0<z≤2;0≤d≤0.2; z−d≤2; M′ comprises one or more metal ions that together have acombined average oxidation state of +3; and M″ comprises one or moremetal ions that together with the Mn and excess proportion, d, oflithium, have a combined average oxidation state of +3.5; and whereinthe Li_(1+d)Mn_(2-z-d)M″_(z)O₄ component comprises a spinel crystallattice structure; the LiM′O₂ component thereof comprises a layeredcrystal lattice structure; at least one of M′ and M″ comprises Co; andthe spinel and layered structures are integrated together into a singlecomposite structure.
 2. The electrode material of claim 1, wherein0.85≤y<1.
 3. The electrode material of claim 1, wherein 0.9≤y<1.
 4. Theelectrode material of claim 1, wherein 0.85≤y≤0.9.
 5. The electrodematerial of claim 1, wherein M′ comprises at least one metal selectedfrom the group consisting of Mn, Ni, and Co; and M″ comprises at leastone metal selected from the group consisting of Ni and Co.
 6. Theelectrode material of claim 5, wherein M′ further comprises at least onemetal selected from the group consisting of Al, Mg, Li, and a first orsecond row transition metal other than Mn, Ni and Co; and M″ furthercomprises at least one metal selected from the group consisting of Al,Mg, and a first or second row transition metal other than Mn, Ni and Co.7. The electrode material of claim 1, wherein 0<d≤0.2; 0.2<z≤0.6; and M″comprises Ni, Co, or a combination thereof.
 8. The electrode material ofclaim 1, wherein M″ comprises at least one metal selected from Ni andCo.
 9. The electrode material of claim 1, wherein M′ comprises Mn andNi.
 10. The electrode material of claim 9, wherein M′ further comprisesCo.
 11. The electrode material of claim 1, wherein the spinel component,Li_(1+d)Mn_(2-z-d)M″_(z)O₄, comprises Mn, Ni, and Co.
 12. The electrodematerial of claim 1, wherein M′ comprises Mn and Ni; and the spinelcomponent, Li_(1+d)Mn_(2-z-d)M″_(z)O₄, comprises Mn, Ni, and Co.
 13. Theelectrode material of claim 1, wherein M″ comprises at least one metalselected from the group consisting of Ni and Co; d>0; and 2-d-z>0. 14.The electrode material of claim 1, wherein M″ comprises Ni and Co; Coconstitutes about 1 atom percent to about 30 atom percent of transitionmetals in spinel component, Li_(1+d)Mn_(2-z-d)M″_(z)O₄; and thecombination of Mn and Ni constitutes about 70 atom percent to about 99atom percent of the transition metals in the spinel component.
 15. Theelectrode material of claim 14, wherein the combination of Mn and Niconstitutes about 80 atom percent of the transition metals in the spinelcomponent and Co constitutes about 20 atom percent of the transitionmetals in the spinel component.
 16. The electrode material of claim 14,wherein the spinel component constitutes about 50 atom percent Mn, about30 atom percent Ni, and about 20 atom percent Co of the transitionmetals in the spinel component.
 17. The electrode material of claim 1,wherein the Li, Mn, M′ and M″ cations are partially disordered overoctahedral and tetrahedral sites of the layered and spinel crystallattice structures of the composite lithium metal oxide structure.
 18. Apositive electrode for a lithium electrochemical cell comprising a layerof the electrode material of claim 1 in contact with a metal currentcollector.
 19. A lithium electrochemical cell comprising the positiveelectrode of claim 18 and a negative electrode in contact with anon-aqueous electrolyte comprising a lithium salt.
 20. A lithium batterycomprising a plurality of the electrochemical cells of claim 19connected together in series, parallel, or both.